Unify test cluster infrastructure by using Rust cluster in Python tests

[Arnav-panjla]

Purpose

Linked issue: close #394

Replace Python test setup based on CLI subprocess with direct Rust test cluster integration for simpler and more reliable testing.

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Brief change log

• Added fluss-test-cluster dependency in bindings/python/Cargo.toml
• Added FlussTestCluster (bindings/python/src/test_cluster.rs):
  • wraps FlussTestingClusterBuilder::build_detached()
  • exposes start, stop, stop_by_name, bootstrap_servers, sasl_bootstrap_servers
• Registered class in bindings/python/src/lib.rs
• Refactored Python test setup:
  • removed subprocess / CLI / file lock logic
  • use FlussTestCluster.start directly
  • cleanup via pytest_unconfigure → stop_by_name

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Tests

• Python tests now use in-process Rust cluster manager
• Removed CLI dependency and JSON parsing
• Verified with test runs

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API and Format

API Change: Yes

• New FlussTestCluster exposed in Python bindings

Storage Format: No

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Documentation

No